instance method `mattr_accessor`

Ruby on Rails 6.1.7.10

Since v2.2.3

Available in: v2.2.3 v2.3.18 v3.0.20 v3.1.12 v3.2.22.5 v4.0.13 v4.1.16 v4.2.9 v5.2.8.1 v6.0.6 v6.1.7.10 v7.0.10 v7.1.6 v7.2.3 v8.0.4 v8.1.2

Compare with:

mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk)

Defines both class and instance accessors for class attributes. All class and instance methods created will be public, even if this method is called with a private or protected access modifier.

module HairColors
  mattr_accessor :hair_colors
end

class Person
  include HairColors
end

HairColors.hair_colors = [:brown, :black, :blonde, :red]
HairColors.hair_colors # => [:brown, :black, :blonde, :red]
Person.new.hair_colors # => [:brown, :black, :blonde, :red]

If a subclass changes the value then that would also change the value for parent class. Similarly if parent class changes the value then that would change the value of subclasses too.

class Citizen < Person
end

Citizen.new.hair_colors << :blue
Person.new.hair_colors # => [:brown, :black, :blonde, :red, :blue]

To omit the instance writer method, pass instance_writer: false. To omit the instance reader method, pass instance_reader: false.

module HairColors
  mattr_accessor :hair_colors, instance_writer: false, instance_reader: false
end

class Person
  include HairColors
end

Person.new.hair_colors = [:brown]  # => NoMethodError
Person.new.hair_colors             # => NoMethodError

Or pass instance_accessor: false, to omit both instance methods.

module HairColors
  mattr_accessor :hair_colors, instance_accessor: false
end

class Person
  include HairColors
end

Person.new.hair_colors = [:brown]  # => NoMethodError
Person.new.hair_colors             # => NoMethodError

You can set a default value for the attribute.

module HairColors
  mattr_accessor :hair_colors, default: [:brown, :black, :blonde, :red]
end

class Person
  include HairColors
end

Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]

Parameters

syms rest
instance_reader key = true
instance_writer key = true
instance_accessor key = true
default key = nil
blk block

Source

# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 200
  def mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk)
    location = caller_locations(1, 1).first
    mattr_reader(*syms, instance_reader: instance_reader, instance_accessor: instance_accessor, default: default, location: location, &blk)
    mattr_writer(*syms, instance_writer: instance_writer, instance_accessor: instance_accessor, default: default, location: location)
  end

Defined in activesupport/lib/active_support/core_ext/module/attribute_accessors.rb line 200 · View on GitHub · Improve this page · Find usages on GitHub

Defined in Module

Signature

Parameters